Welcome to TalkBass harmologna
Originally Posted by Andyman001
I've never worked on an upright/double bass before, I'd have to see it to comment further.
can you upload a picture or two?
+1 for pics, but almost all the "real" DB tuners I've seen have been the ones Leo did copy "his" design from
Soldering/brazing works well if the leaf is just worked itself loose, but often that repair looks a bit messy afterwards.
A "modern" way is either epoxy or CA.
Both are fully reversible, easy to clean and are IME very permanent solutions unless the instrument gets smacked around a lot.
If the leaf is what rattles, and was originally just riveted in place, a good machinist or luthier will be able to retighten (or replace) the rivet, but a DIYer usually just makes the rattling worse. Not to mention the looks
OTOH, if the shaft has worked itself loose in the plate, that takes considerably more work to repair. But is perfectly doable.
So, help us to help You and do post some pics.